Question

如何从单个表合并多个查询？这是我当前的查询，但输出错误

   SELECT     
        Employees201MasterFile.Name, CASE WHEN SUM(StockTrans.conv_bal) IS NULL THEN 0 ELSE SUM(StockTrans.conv_bal) END AS 'curMonthBal',
        CASE WHEN SUM(StockTrans.conv_bal) IS NULL THEN 0 ELSE SUM(StockTrans.conv_bal) END AS 'prevMonthsBal'
   FROM 
        Employees201MasterFile INNER JOIN
        Stocktrans ON Employees201MasterFile.Name = Stocktrans.Customer
   WHERE
        stocktrans.date >= '12/01/15' AND stocktrans.date <= '12/31/15'
        OR stocktrans.date < '12/01/15' AND stocktrans.conv_bal <> 0
   GROUP BY Employees201MasterFile.Name
---------------------------------------------------------------
name    currentMonthBalance   prevMonBal
EMP1    114                   114           
EMP2    182                   182   
EMP3    29                    29

输出应为

---------------------------------------------------------------
name    currentMonthBalance   prevMonBal
EMP1    114                   366           
EMP2    0                     182           
EMP3    29                    0

我想要的输出：伪查询：

if employee has balance on this month (december 1 - 31, 2015 only), sum all balance for this month ELSE return 0
--> this will be the currentMonthBalance

if employee has previous month balance, sum all previous balance except (december 2015) the selected month ELSE return 0
--> this will be the prevBalance

这可能在SQL Query上吗？

Answer 1

您可以使用条件聚合执行此操作：

DECLARE @fromMonth AS DATE = '20151201'

SELECT     
    emf.Name, 
    SUM(CASE WHEN st.date >= @fromMonth AND st.date < DATEADD(MONTH, 1, @fromMonth) THEN st.conv_val ELSE 0 END) AS [curMonthBal],
    SUM(CASE WHEN st.date < @fromMonth THEN st.conv_val ELSE 0 END) AS [prevMonthsBal]
FROM Employees201MasterFile AS emf
INNER JOIN Stocktrans AS st
    ON emf.Name = st.Customer
WHERE
    st.date < DATEADD(MONTH, 1, @fromMonth)
GROUP BY emf.Name

您应该在表上使用有意义的别名，以便于阅读。

Answer 2

你的查询：

SELECT x.Name, curMonthBal, prevMonthsBal FROM
(
   SELECT     
        Employees201MasterFile.Name, CASE WHEN SUM(StockTrans.conv_bal) IS NULL THEN 0 ELSE SUM(StockTrans.conv_bal) END AS 'curMonthBal'
   FROM 
        Employees201MasterFile INNER JOIN
        Stocktrans ON Employees201MasterFile.Name = Stocktrans.Customer
   WHERE
        stocktrans.date >= '12/01/15' AND stocktrans.date <= '12/31/15'
        AND stocktrans.conv_bal <> 0
   GROUP BY Employees201MasterFile.Name
) x
INNER JOIN
(
   SELECT     
        Employees201MasterFile.Name,
        CASE WHEN SUM(StockTrans.conv_bal) IS NULL THEN 0 ELSE SUM(StockTrans.conv_bal) END AS 'prevMonthsBal'
   FROM 
        Employees201MasterFile INNER JOIN
        Stocktrans ON Employees201MasterFile.Name = Stocktrans.Customer
   WHERE
        stocktrans.date < '12/01/15' AND stocktrans.conv_bal <> 0
   GROUP BY Employees201MasterFile.Name
) y
ON  x.Name = y.Name

如何从单个表合并多个查询？

2 个答案: